Endocrine disruptors (EDs) are a group of molecules capable of altering normal endocrine function in animals and humans. We and others have demonstrated that in utero exposure to EDs causes obesity and abnormal glucose homeostasis in the offspring. Phthalates are an important group of EDs that are used in a diverse range of industrial applications leading to common exposure risk in humans. One major phthalate is di-(2-ethylhexyl)-phthalate (DEHP), a widely used compound for which dietary exposure (food processing, packaging) likely represents the main source of contamination for the general population. Both human and animal models show a link between phthalate exposure and the development of obesity and the metabolic syndrome. Similar to these studies, our preliminary data show that DEHP exposure through the diet in physiologically relevant doses prior to and during pregnancy and lactation alters DNA methylation in fetal liver, increases body weight in adult offspring in a sex-specific manner. It is becoming increasingly evident that the periconceptional stage also represents a window of susceptibility to environmental exposures on the offspring. While the mechanisms responsible for the transfer of metabolic memory from the oocyte to the offspring remain to be elucidated, 2 plausible possibilities are epigenetic dysregulation and abnormal mitochondria. Further, we and others have shown that epigenetic changes and abnormal mitochondrial function in key organs such as the liver, -cell and muscle have been linked to development of obesity and diabetes. Thus, we hypothesize that a preconception exposure to DEHP, similar to a gestational exposure, results in an abnormal metabolic phenotype in the offspring by altering either the epigenetic profile and or mitochondrial function in the oocyte. Thus we propose the following specific aims: Aim 1 will determine whether a preconception exposure to biologically relevant doses of DEHP results in a similar offspring phenotype as a gestational exposure. Aim 2 will determine the molecular and cellular mechanisms by which the two different exposure windows result in a similar or different metabolic phenotype in the offspring. We will profile the transcriptome by RNA-seq and the epigenome by ATACseq and bisulfite-seq in the oocyte and key tissues in the offspring. We will then determine the effects of DEHP on key aspects of mitochondrial function such as respiration, ATP, ROS, and morphology. The proof of the principle of preconception programming by environmental contaminants may change our awareness of critical assessment of the risk of such compounds.